Bethan, four fairly steady months
28, 30, 27 and 29 days
Average 28.5 days. Range 27 to 30 across 4 cycles, inside a common adult band.
Cycle Length Calculator
Cycle length is the number of days from the start of one period to the start of the next. Log a few lengths. We show the average and the shortest-to-longest spread. It is a diary average, not a hormone test, not contraception and not a diagnosis.
Your details
Enter the length of recent cycles in days. Blank boxes are ignored.
What is this calculator?
Cycle length is the number of days from the start of one period to the start of the next. Log a few lengths. We show the average and the shortest-to-longest spread. It is a diary average, not a hormone test, not contraception and not a diagnosis.
How it works
- Type each recent cycle in days. You need at least one.
- We average them and show the range.
- Take the numbers to a GP or the period calculator if you want dates, not only an average.
Common questions
What is the cycle length calculator?
It averages the cycle lengths you type and shows the spread. It cannot see you and cannot diagnose.
What is a typical cycle?
Many adults sit somewhere near 21 to 35 days. Plenty of healthy people sit outside that in some months.
Can I use this as contraception?
No. Rhythm methods fail. Use contraception you have chosen with a clinician if you need it.
When should I see a GP?
Very short, very long, suddenly changed, or painful cycles are worth a conversation. So is bleeding that soaks through or makes you dizzy.
Example scenarios
Habiba, a longer stretch
35, 38, 33 and 36 days
Average 35.5 days. Range 33 to 38. Worth a GP chat if that pattern persists.
Ceri, three shorter cycles
24, 26 and 25 days
Average 25 days. Range 24 to 26 across 3 cycles, still inside a common band.
Understanding your results
One odd month is common. A new pattern that lasts is the reason to talk to a person. The period and ovulation calculators turn an average into dates if that is the next job.
About this result
Guidance only. Calculations run in your browser. Numbers are estimates, not a diagnosis.
How we calculate
Average, minimum and maximum of the cycle lengths you enter. Blanks are ignored.
Sources
Limitations
- Not contraception.
- Not a fertility or PCOS diagnosis.
- Self-logged days only.
When to seek help
Speak to a GP or call NHS 111 if bleeding is very heavy, cycles change suddenly, or you are worried. Call 999 if you collapse or bleed heavily and feel very unwell.
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